Bone fixing device and method for distracting a fracture and jig and method for insertion of a bone fixing device

ABSTRACT

A bone fixing device and a method of distracting a fracture are described. The bone fixing device has threads at both a leading end and a trailing end, and the pitch of the threads are greater at the trailing end. This causes the leading end of the bone fixing device to travel more slowly through the bone than the trailing end, which loads the threads of the screw to put the screw under compression, so that the threads bite more effectively into the bone. A jig and method for insertion of two bone fixing devices are also described. The jig defines parallel planes of insertion which cross when viewed in a direction perpendicular to the parallel planes.

The present invention concerns an apparatus and method for treating afracture in a bone, especially but not exclusively for treating a wristfracture.

When a wrist bone breaks, it often fractures into many fragments on thedorsal side of the wrist, whilst leaving a fairly clean break on thelower side. A typical broken wrist is shown in FIG. 1. Distal boneportion 12 needs to be held fixed relative to proximal bone portion 14in the position shown in FIG. 1, so that the bone portions 12, 14 do notheal in the position shown in FIG. 2. Further bone fragments generallyfloat in the space designated 16. These will fuse with bone portions 12,14 as the fracture heals.

One method of treating a wrist fracture involves attaching a metal frameto the outside of the wrist, spanning the wrist joint. Pins typicallyextend from the frame into the bone portions on each side of thefracture. This can be an invasive method, and can immobilise the jointfor a long period, resulting in a very stiff joint once the fracture hashealed. A further alternative method involves fixing the fracture usingplates and screws. All of these methods are very invasive, in some casestotally preventing movement of the joint and are likely to be veryinconvenient to the patient.

According to the present invention there is provided a bone fixingdevice for distracting a fracture, the bone fixing device having a bodywith a leading end and a trailing end, the bone fixing device beingthreaded at least at the leading end and at the trailing end; whereinthe pitch of the threads at the trailing end is greater than the pitchof the threads at the leading end.

By “distracting a fracture” we mean causing a partial movement offracture fragments away from one another.

Not allowing the bone portions to move towards one another isadvantageous, especially for fractures such as that shown in FIG. 1,where the lower side of the fracture is a clean break, and the otherside is broken into multiple fragments. If the bone portions were notmaintained by the fixing device, the bone portions could pivot aroundthe clean break and out of alignment.

Distraction of the fracture (i.e. loading the bone portions to push thebone portions apart relative to each other) has been discovered to bedesirable, as putting the bone portions in tension causes the boneportions to grip the threads of the fixing device more firmly, whichreduces the likelihood of the fixing device working itself loose.Distracting the fracture loads the threads of the screw so that thescrew is under compression and the threads bite more effectively intothe bone.

The greater the pitch of the screw threads, the quicker the axialprogress through the bone. Therefore, if the pitch of the screw threadsat the trailing end (e.g. at the head) of the fixing device is greaterthan the pitch at the leading end (e.g. at the tip that is driventhrough the bone first), the trailing end will progress more quicklythrough the bone than the leading end, which will push the two boneportions apart to distract the fracture.

In the following description, the “leading” end and the “tip” end bothrefer to the end of the fixing device which penetrates the bone first.The “trailing” end and the “head” end both refer to the opposite end ofthe fixing device from the leading end.

Typically, the fixing device is self-drilling and has a self-tappingtip.

Optionally, the trailing end of the fixing device does not have aradially-extending head, i.e. unlike a typical screw, the head of thefixing device is simply an axial extension/continuation of the leadingend of the fixing device; which is flush with the rest of the fixingdevice.

Optionally, the trailing end of the fixing device has a larger diameterthan the leading end.

Typically, the fixing device diameter increases uniformly towards thetrailing end. Alternatively, the fixing device comprises two portions ofdifferent diameters.

Typically, threads are provided along the entire length of the fixingdevice. Alternatively, threads are provided only at the leading andtrailing ends of the fixing device.

Optionally, the screw threads increase uniformly in pitch towards thehead of the fixing device. Optionally, the fixing device comprises twoportions each having screw threads of a different pitch.

Optionally, the screw threads have a longitudinal axis and at least oneside of at least one of the screw threads has a portion steeply inclinedrelative to the axis.

“Steeply inclined” is intended to encompass both a side which isperpendicular to the axis and a side having a portion that is steeplysloping. “Steeply inclined” can include the meaning substantiallyperpendicular.

The screw threads having one or more steeply inclined portions make thefixing device difficult to remove from the bone on application of anaxial force, without rotating the fixing device. This is especiallyadvantageous for use in soft bone, (such as in elderly patients) wherethe fixing device could otherwise accidentally fall out or fail to holdthe fracture reduction.

Typically, the screw threads include at least one side steeply inclinedrelative to the axis in each axially-facing direction. Typically, eachthread has a steeply inclined side in at least one axially-facingdirection. Typically, the steeply inclined sides face the opposing endsof the fixing device. Typically, the other sides of the threads slopemore gradually than the steeply inclined sides, and these sloped sidestypically face one another i.e. towards the centre of the fixing device.

Typically, the screw is made from a bioabsorbable material. Thebioabsorbable material may comprise polylactic acids, polyglycolicacids, or a combination of both. Alternatively, the screw is made frommetal. The invention is not limited to any of these exemplary materials.

Preferably, the screw has a coating, e.g. a dip coating. Typically, thecoating comprises hydroxyapatite. The presence of hydroxyapatite(naturally found in bone tissue) encourages new bone growth in thesurrounding vicinity of the screw.

According to a second aspect of the present invention there is provideda method of treating a fracture by distracting the fracture to hold thebone portions apart under tension.

The method is optionally achieved by inserting a bone fixing deviceaccording to the first aspect of the invention into the bone.

Optionally, the fixing device is cannulated and the method includes thesteps of inserting a guide wire into the bone and subsequently insertingthe fixing device over the guide wire.

Optionally, the fixing device is self-drilling and/or has a self-tappingtip and the bore is formed by the fixing device, rather than a drill.

Optionally, the method includes using a jig to aid alignment of thefixing device and/or any guide wire and/or any drill or tap used.

According to a third aspect of the invention there is provided a fixingdevice for insertion into at least two bone portions to treat afracture, the fixing device having a body with formations on its outersurface adapted to maintain the relative position of the bone portions;and an axial bore extending through the body.

According to a fourth aspect of the invention there is provided a fixingdevice for insertion into at least two bone portions to treat afracture, the fixing device having a body with formations on its outersurface adapted to maintain the relative position of the bone portions;and a self-tapping tip.

According to a fifth aspect of the invention there is provided a methodof treating a fracture, comprising engaging a fixing device into atleast two bone portions of the fracture to maintain the relativeposition of the bone portions.

According to a sixth aspect of the present invention there is provided afixing device for insertion into at least two bone portions to treat afracture, the fixing device having a body with formations on its outersurface adapted to distract the bone portions.

According to a seventh aspect of the present invention there is provideda method of treating a fracture, comprising inserting a fixing deviceinto at least two bone portions of the fracture, whereby insertion ofthe fixing device holds the two bone portions apart under tension todistract the fracture.

This invention also relates to a jig to aid insertion of a bone fixingdevice into a bone to treat a fracture. This invention relatesespecially but not exclusively to a jig which aids the relativealignment of at least two bone screws.

Bones often fracture into a plurality of bone fragments. In this case,it is helpful to insert two screws along different line of insertion, soas to span most of or all of the fragments. It is highly undesirable ifthese two screws collide with each other, because this could prevent thesecond screw from being fully inserted into the bone, and could alsoforce the first screw out of position. If this happens, the second screwwould have to be removed and a new hole made.

Therefore, to avoid this problem, the second screw is typically insertedat a safe distance away from the first screw so that there is anegligible chance of a collision. However, once the screws have beeninserted, the only support keeping the screw in the bone is frictionbetween the bone and the screw threads. In patients with fragile crumblybone, e.g. some elderly patients, this friction may not be sufficient,and the bone screws may work themselves loose. This could further damagethe bone and additional surgery may be required.

According to a eighth aspect of the invention there is provided a jigfor positioning first and second bone fixing devices, the jig definingfirst and second lines of insertion for the first and second bone fixingdevices respectively, wherein the lines of insertion lie in parallelplanes and wherein the lines of insertion cross when viewed in adirection perpendicular to the parallel planes.

Provision of the jig allows the second line of insertion to be definedvery accurately with respect to the first line of insertion. Because thelines of insertion are in parallel planes, they can never intersect, andthe possibility of bone fixing devices colliding with each other isreduced.

Optionally, more than two lines of insertion could be defined by thejig.

Typically, the bone fixing devices are at least partially threaded.Preferably, the bone fixing devices comprises bone screws.

Preferably, the parallel planes are relatively close to one another.Preferably, the parallel planes have a minimum separation equal to thediameter of the bone fixing device. If the fixing device comprises athreaded fixing device, e.g. a bone screw, preferably the parallelplanes have a minimum separation equal to the outer thread diameter ofthe bone fixing device. Such embodiments can ensure that the bone fixingdevices will not collide.

Some such embodiments can provide that the bone fixing devices interact,thus providing an additional connection to each other, which helps tohold the bone fixing devices in the bone. “Interact” is used in thesense that the bone fixing devices can touch and can lean against eachother, one fixing device effectively buttressing and supporting theother.

Preferably, the orientation of the second line of insertion is variablerelative to the orientation of the first line of insertion. Preferably,the second line of insertion is translatable relative to the first lineof insertion.

“Translation” is used throughout the specification to mean not onlymovement along a straight line, but also movement along an arcuate path.“Translational movement” is used as a way of differentiating betweenrotational movement about an axis.

Preferably, the jig includes an arm that extends in a lateral directionwith respect to at least one of the lines of insertion.

Preferably, the arm is arcuate.

Preferably, at least a part of the arm has a planar surface that isparallel to the parallel planes of the lines of insertion. optionally,at least a part of the arm has a planar surface that is co-planar withone of the parallel planes of the lines of insertion.

Preferably, the first and second lines of insertion are defined byrespective first and second guide means coupled to the arm. Typically,the first and second guide means have bores that serve to align the pathof the guide wire or bone fixing device with the desired line ofinsertion. In some embodiments, the guide means may include at least oneguide sleeve received in the bore of the guide means and the guidesleeve can be slidably and/or rotatably mounted in the bore so that itis releasably coupled to the arm. Typically, the arm is rotatablymounted relative to the guide means so that the arm can pivot around theaxis of the guide means.

A guide means can be anything which can guide the path of a guide wireand/or a bone fixing device. Typically, the first and second guide meanscan include first and second guide sleeves. Optionally, each of thefirst and second guide means comprises a plurality of concentricsleeves. However, in more basic embodiments, an apertured section of thearm can suffice, and separate guide sleeves are not necessary.

Typically, the first and second guide means are adapted to receive guidewires and/or bone fixing devices. The invention is not limited to theuse of guide wires because in some embodiments, the first and secondguide means can directly guide the bone fixing devices into the bone.

Optionally, the jig includes a spacer adapted to space the parallelplanes of the lines of insertion apart from each other.

Typically, the spacer is a separate component which is coupled to thearm.

Optionally, the spacer comprises a block having a guide bore adapted toreceive a guide means. Preferably, the guide means can be slidablymounted in the guide bore, and can optionally rotate relative thereto.

Optionally, the spacer has an attachment bore and the spacer is coupledto the arm by an attachment device inserted through the attachment borein the spacer and also into/through the arm. Preferably, the spacer isrotatably mounted on the arm. Typically, the attachment device comprisesa bolt and a nut; the bolt and nut connection can be loosened to allowrotation of the spacer relative to the arm. After selection of therequired angle, the nut can be tightened to fix the rotational positionof the spacer relative to the arm.

Optionally, an elongate aperture is provided in the arm, and the spaceris moveable along the elongate aperture. If the attachment device is abolt and a nut, the bolt can be loosened to allow translation of thespacer relative to the arm using the elongate aperture, and thentightened again to restrict further translational movement once aposition has been selected.

Optionally, the arm may be extendible to allow relative translationalmovement of the first and second guide means.

Typically, the position of one of the guide means is defined by the armand the position of the other guide means is defined by the spacer, suchthat rotating the spacer relative to the arm varies the orientation ofthe second guide means relative to the first guide means, andtranslating the spacer along the arm varies the distance between thefirst and second guide means.

Rotational and translational capabilities are not essential. Embodimentswhere the first and second lines of insertion are fixed relative to eachother are also covered by the invention (for example, if the first andsecond guide means are both fixed relative to the arm).

The spacer is not necessarily a separate component. Alternatively, thespacer could comprise a part of the arm. For example, the arm couldcomprise a first portion and a second portion having parallel planarsurfaces, wherein the second portion is stepped relative to the firstportion. In such embodiments, the step in the arm can function as aspacer to space the two parallel surfaces of the first and second partsof the arm from each other, and these parallel surfaces can define theparallel planes of the first and second lines of insertion.

In such embodiments, the position of the second guide means may be fixedin angular orientation and/or translational position relative to thefirst guide means (apart from any optional slidable mounting to thearm). For example, such an embodiment may be made by attaching a firstguide means to one end of the arm and a second guide means to the otherend of the arm on the other side of the stepped portion. However, inpreferred embodiments, at least one of the guide means is rotatablymounted on the arm. This could be achieved, for example, by hingedlymounting the second guide means to the arm. In this way, the relativeangles of insertion of the two bone fixing devices can be selected.

In some embodiments, a stepped arm and a separate spacer component canboth be used in conjunction to provide the two parallel planes of thelines of insertion.

In all embodiments, the arm may optionally have an elongate slot toenable relative translational movement of the first and second guidemeans.

In all embodiments, the arm may optionally be extendible to enablerelative translational movement of the first and second guide means.

According to a ninth aspect of the present invention there is provided amethod of positioning first and second bone fixing devices relative toeach other, the method including the steps of defining first and secondlines of insertion for the first and second bone fixing devicesrespectively; wherein a jig is used to define the position of the secondline of insertion relative to the first line of insertion such that thelines of insertion lie in parallel planes and such that the lines ofinsertion cross when viewed in a direction perpendicular to the parallelplanes.

Preferably, this method is performed using the jig of the eighth aspectof the invention.

Preferably, the separation of the parallel planes is greater than orequal to the diameter of the bone fixing devices. Optionally, the fixingdevices are at least partially threaded and the separation of theparallel planes is greater than or equal to the outer thread diameter ofthe bone fixing devices.

Optionally, the bone fixing devices are inserted at locations very closeto each other. Optionally, the bone fixing devices are inserted atlocations in which they are in contact with each other. Optionally, thebone fixing devices are at least partially threaded, and the threads arein contact with each other or narrowly miss each other.

Typically, the jig includes first and second guide means which definerespective lines of insertion of the first and second bone fixingdevices, and the method includes the step of translating and/or varyingthe orientation of one guide means relative to the other. Preferably,the method includes the step of fixing the two guide means at a selectedorientational and translational position. The guide means can be guidesleeves.

Optionally one or each of the first and second guide means comprises aplurality of concentric sleeves. An inner sleeve may be used to insert aguide wire. An intermediate sleeve may be used to insert a drill overthe guide wire to drill a hole for the fixing device. An outer sleevemay be used to guide the insertion of the fixing devices (and anyoptional tap used). Alternatively, the fixing devices may be selfdrilling/self tapping, rendering the use of a drill/tap and theintermediate guide sleeve unnecessary.

As apparent from the above, the jig does not include the guide sleeves,as the guide sleeves are themselves attachable to and removable from thejig. Any guide sleeves/drill sleeves can be used with the jig.

Typically, the method includes the step of inserting first and secondguide wires into the bone along respective first and second lines ofinsertion. Typically, the position of the first line of insertion isselected and the first guide wire and then optionally the first fixingdevice are inserted without using the jig (e.g. using standarddrill/guide sleeves). The jig is then fitted over the projecting part ofthe guide wire and used to define the second line of insertion for thesecond guide wire and the second fixing device, which are then insertedusing the second guide means.

Typically the method includes the additional step of inserting first andsecond bone fixing devices over the first and second guide wires intothe bone.

Typically, at least the second fixing device is inserted using the jig,for example by inserting the second fixing device through a guide sleevecoupled to the jig. The guide sleeve protects the surrounding tissuesfrom damage by the fixing device and the drill. Alternatively, the jigmay be removed before insertion of one or both of the fixing devices,and a separate guide sleeve(s) may be used to guide the fixing devicealong the lines of insertion already defined by the guide wires.

Alternatively, the first and second bone fixing devices could beinserted via the guide means into the bone, without the need for anyguide wires.

According to a tenth aspect of the present invention there is provided amethod of positioning first and second bone fixing devices in a bonesuch that they just touch each other.

Embodiments of the invention will now be described, by way of exampleonly, and with reference to the following drawings, in which:

FIG. 1 shows a side view of a broken wrist with bone portions in thecorrect alignment to heal;

FIG. 2 shows a side view of a broken wrist, with bone portionsincorrectly aligned;

FIG. 3 shows a cross-section of two bone portions with a guide wireinserted through both bone portions;

FIG. 4 shows a cross-section of the bone portions of FIG. 3, with afixing device inserted through the portions;

FIG. 5 shows a side view of a further alternative embodiment of a fixingdevice having threads of varying pitch;

FIG. 6 shows a side view of a further alternative embodiment, havingthreads of different pitches and two portions of different diameters;

FIGS. 7 a and 7 b show a further embodiment, having steeply slopingscrew threads of varying pitch;

FIG. 8 shows a side view of a further embodiment, having steeply slopingscrew threads of varying pitch and a varying diameter;

FIGS. 9 a and 9 b show sectional views of a further embodiment, havingrectangular threads of varying pitch;

FIG. 10 shows a sectional view of a further embodiment, havingrectangular threads of varying pitch and varying diameter;

FIGS. 11 a and 11 b show a further embodiment, having perpendicularscrew threads in each axially-facing direction, the threads having avarying pitch;

FIG. 12 shows a side view of a further embodiment, having perpendicularscrew threads in each axially-facing direction of varying pitch andvarying outer diameter;

FIG. 13 shows a cross-sectional view of a jig of the present inventionbeing used to insert guide wires into a bone;

FIG. 14 shows a cross-section view of part of a second embodiment of theinvention;

FIG. 15 shows a schematic view from above of two fixing devices insertedalong respective lines of insertion I1, I2, wherein the distance apartof the parallel planes of the lines of insertion equals the diameter ofthe fixing device;

FIG. 16 shows a schematic view similar to FIG. 15, wherein the fixingdevices are threaded and the spacing of the parallel planes equals theouter (thread) diameter of the fixing devices;

FIG. 17 shows a schematic top view of a modified jig having a steppedarm;

FIG. 18 shows a schematic top view of a modification to the FIG. 17stepped arm jig;

FIG. 19 shows a schematic top view of an alternative jig having twospacers and a non-stepped arm;

FIG. 20 shows a sectional view of a further embodiment, having steeplysloping screw threads of consistent pitch;

FIG. 21 shows a sectional view of a further embodiment, havingrectangular threads of consistent pitch; and

FIG. 22 shows a sectional view of a further embodiment, havingperpendicular screw threads in each axially-facing direction.

Referring now to the drawings, FIG. 5 shows a screw 100 having a head120, a root 118 and screw threads 112 all the way along its length. Thescrew 100 is tapered, i.e. the diameter of root 118 and the outerdiameter of screw threads 112 typically both increase uniformly towardsthe head 120. Such tapering can allow the screw 100 to be more easilyinserted into a pilot hole; in some cases, a pilot hole may not even berequired. Furthermore, the increasing diameter of the root 118 and thethreads 112 towards the head end of screw 100 will urge the root 118against previously uncut portions of bone, and the threads will cut intonew bone which was not previously cut by the smaller diameter threads,both of which will secure the screw 100 more firmly into the bone thancould be achieved with other designs.

The pitch of screw threads 112 increases uniformly towards the head 120.The pitch of the threads is typically in the range 1 mm to 2 mm at theleading (tip) end, and 2 mm to 4 mm at the trailing (head) end. Thescrew 100 will typically cause a relative distraction of bone portions12, 14 of 1 mm to 2 mm per rotation.

The head 120 is flush with the outer surface of root 118 so that thehead 120 is an axial continuation of the body of the screw 100 and itdoes not project radially outward of the root 118. Alternativeembodiments may have an outwardly projecting head. In this example,screw 100 is cannulated to allow insertion over a guide wire (notshown). However, non-cannulated embodiments can also be used. The head120 may have an aperture for insertion of an Allen key or other torquetool. The screw 100 preferably has a self-drilling, self-tapping tip.

Although screw 100 shown here has screw threads 112 extending along thewhole of its length, alternative embodiments (not shown) may have screwthreads only at particular portions, and not at others, for example, atleading and trailing ends, with a mid-portion remaining unthreaded.

Alternatively, the root diameter could be constant, and the outer threaddiameter alone could increase towards the head 40 (examples of suchembodiments are found in FIGS. 8, 10 and 12, described below).

FIG. 6 shows a screw 200 (having a root 218 and a head 220), which issimilar to screw 100, in that the root 218 and threads vary in diameter.However, instead of varying uniformly, screw 200 is divided into twoportions of different diameter: a trailing portion 230 having screwthreads 235 and a leading portion 240 having screw threads 245. Both thediameter of the root 218 and the outer diameter of the screw threads235, 245 are different between each of the two portions, but are uniformwithin each portion 230, 240. The trailing portion 230 has a largerdiameter root (of around 2 mm to 4 mm) and a larger outer diameter ofscrew thread (of around 3 mm to 6 mm) than the leading portion 240 (3 mmto 5 mm and 4 mm to 7 mm for root and thread respectively). Threads 230have a constant pitch, as do threads 240, but the pitch of screw threads230 is approximately 2-4 mm, which is greater than the pitch of screwthreads 240 at approximately 1-2 mm. Thus, the diameter of the root andthe threads, and the thread pitch varies in the same way as for screw100, except that the variation is abrupt between the two portions 230,240, instead of continuous. As with screw 100, embodiments of screw 200may be cannulated; may have a self-drilling, self-tapping tip; may havea non-threaded mid-portion; and may have a head which does not projectoutwardly of its root. The arrangement shown in FIG. 6 could of coursebe modified so that the sides of the root of the screw 200 are parallelso that the diameter of the root is uniform for the length of the screw200. Such a modification could optionally have the variations in thediameter and pitch of the threads that are shown in FIG. 6.

In use, the bone portions 12, 14 are first aligned into the correctposition shown in FIG. 1. Next, a K-wire 24 is typically inserted intothe bone to span the fracture, with opposite ends of the K-wire 24engaging respective bone portions 12, 14. An image intensifier(apparatus which produces low intensity x-rays) is typically used tocheck that the K-wire 24 is correctly positioned, as shown in FIG. 3.The length of protruding guide wire is measured and deducted from theknown length of the wire to indicate the correct screw length.

Next, the screw 100, 200 is inserted over the K-wire 24 and screwed intothe bone portions 12, 14, e.g. by using an Allen key, as shown in FIG.4. If the screw 100, 200 is not self-drilling and/or self-tapping, thena hole would have to be drilled and/or tapped before inserting the screw100, 200 e.g. with a cannulated drill inserted over K-wire 24. A jig isoptionally used to align the screw 100, 200 and/or the K-wire, and/orany drill used.

The leading end (tip end) of the screw 100, 200 engages bone portion 14and the trailing end (head end) engages bone portion 12. Since the head120, 220 is merely an extension of the body of screw 100, 200 and itdoes not protrude radially outward from the root 118, the head 120, 220can be driven completely inside bone portion 12 along with the rest ofscrew 100, 200 (see FIG. 4), as opposed to complete insertion beingprevented by a radially-extending head abutting against the exteriorsurface of cortical bone portion 12.

If a screw having a radially-extending head were to be fully insertedinto bone portion 12, when the head abuts the exterior of bone portion12, the head 120, 220 would be held stationary with respect to boneportion 12, whilst the leading end of screw 100, 200 would travelfurther into bone portion 14. This would pull the bone portions 12, 14together, compressing the fracture, as opposed to maintaining ordistracting it.

It would be possible to have a radially-extending head and to avoid theabove problem of compression, by using an alternative embodiment (notshown) wherein the screw 100, 200 is long enough for the head not toabut the outer surface of bone portion 12 when the rest of the screw iscorrectly positioned in bone portions 12 and 14; this embodiment wouldtypically not be fully inserted into the bone portions.

The greater the pitch of the screw threads, the greater the distance thescrew will advance into the bone per rotation of the screw. Therefore,if a screw has screw threads of different pitches on different parts ofthe screw, these different parts of the screw will travel at differentrates. The increase in pitch of the screw threads 112, 230, 240 towardsthe head 120, 220 means that for every rotation of the screw 100, 200,the tip of the screw will progress more slowly through the bone than thehead 120, 220. Therefore, the leading end of the screw 100, 200, withits low-pitch screw threads will advance more slowly through boneportion 14, compared to the trailing (head) end of the screw 100, 200advancing through bone portion 12. This will result in the two boneportions 12, 14 being pushed apart, and the screw 100, 200 being putinto compression between the two bone portions. The more the screw isrotated, the more the bone portions 12, 14 are pushed apart to distractthe fracture.

For example, in the case of screw 200, if the pitch of the screw threads245 is twice the pitch of the screw threads 235, the screw threads 245will advance into the bone twice as quickly as screw threads 235, so forevery 1 mm of axial movement of the leading portion 230, there will be 2mms of axial movement of the trailing portion 240 and therefore the boneportions 12, 14 will have become pushed apart (distracted) by 1 mm.

The screw 100, 200 is driven through the bone until the bone portionshave been distracted sufficiently. The screw 100, 200 can now be left inthe bone in that position until the fracture has healed, or permanentlyas clinically indicated.

Maintaining the position of the bone portions is advantageous,especially for fractures such as that shown in FIG. 1, where the lowerside of the fracture is a clean break, and the other side is broken intomultiple fragments. If the relative positions of the main bone portionsare not maintained by the fixing device, and they are instead pulledtogether, the bone portions could pivot around the clean break, displacethe comminuted fragments in the space 16, and heal out of alignment.

Distraction of the fracture (i.e. loading the bone portions to push thebone portions apart relative to each other) has been discovered to bedesirable, as putting the bone portions in tension causes the boneportions to grip the formations (e.g. screw threads) of the fixingdevice more firmly, which reduces the likelihood of the fixing deviceworking itself loose. Distracting the fracture loads the threads of thescrew so that the screw is under compression and the threads bite moreeffectively into the bone.

Referring now to FIGS. 7 to 12, there are shown screws having modifiedthread profiles. FIG. 7 b shows an enlarged cross-sectional view of asingle screw thread of FIGS. 7 a and 8. Similarly, FIG. 9 b shows anenlarged cross-sectional view of a single screw thread of FIGS. 9 a and10. FIG. 11 b shows an enlarged cross-sectional view of a single screwthread of FIGS. 11 a and 12.

In the screws of FIGS. 7 and 8, both the leading and trailing sides ofthe thread slope between the radially outer tip of the thread and theroot; the slope is very steep. The steeper the slope (i.e. the closer toperpendicular with the root axis) the more difficult it is to remove thescrew from the bone by an axial force. This is because thenear-perpendicular surfaces provide an abrupt resistance to the passageof the screw through the bone, as compared to more gradually slopingsurfaces, where the screw would use the gradual slope to ease its waythrough the bone. Therefore the screws of FIGS. 7 and 8 would be verydifficult to remove from the bone, in either axial direction.

The FIG. 7 screw threads vary in pitch, with the pitch increasingtowards the trailing end (head end). The pitch could vary uniformly, orabruptly. Thus, the FIG. 7 screw is suitable for distracting a fracture.

The FIG. 8 screw has two portions of different root and outer threaddiameter, wherein the thread pitch on the leading portion is smallerthan that of the trailing portion. The pitch of the threads is typicallyin the range 1 mm to 2 mm at the leading (tip) end, and 2 mm to 4 mm atthe trailing (head) end. The FIG. 8 screw will typically cause arelative distraction of bone portions 12, 14 of 1 mm to 2 mm perrotation.

The screws of FIGS. 9 and 10 exhibit an alternative design of screwthread, wherein the threads have sides that are substantiallyperpendicular to the body. The substantially perpendicular sides areshown particularly well in FIG. 9 b. Like the design of threads of FIGS.7 and 8, a screw with these threads would be very difficult to removefrom a bone by axial force in either direction.

The FIG. 9 screw has a constant root diameter, a constant outer threaddiameter, but a varying pitch of thread. The FIG. 9 screw comprises twodiscrete portions of different pitch of thread; however, alternativeembodiments could have a uniformly varying pitch. The pitch of thethreads is typically in the range 1 mm to 2 mm at the leading (tip) end,and 2 mm to 4 mm at the trailing (head) end. The FIG. 9 screw willtypically cause a relative distraction of bone portions 12, 14 of 1 mmto 2 mm per rotation.

The FIG. 10 screw has a constant root diameter, a varying thread pitch,and a varying outer diameter of the thread. The FIG. 10 screw comprisestwo discrete portions of different thread pitch and outer threaddiameter; however, alternative embodiments could have a uniformlyvarying pitch/outer diameter. Alternative embodiments also having avarying root diameter could also be used. The pitch of the FIG. 10threads is typically in the range 1 mm to 2 mm at the leading (tip) end,and 2 mm to 4 mm at the trailing (head) end. The FIG. 10 screw willtypically cause a relative distraction of bone portions 12, 14 of 1 mmto 2 mm per rotation.

The screws of FIGS. 11 and 12 show a further alternative design of screwthread. Each thread has one perpendicular side and one sloping side; thethreads at the leading end of the screw have perpendicular leadingsides, and the threads at the trailing end of the screw haveperpendicular trailing sides. The perpendicular sides are shownparticularly well in FIG. 11 b.

The FIG. 11 screw has threads of varying pitch. The leading and trailingends of the FIG. 11 screw have threads of a constant outer diameter anda constant root diameter. The FIG. 11 screw comprises two discreteportions of different thread pitch; however, alternative embodimentscould have a uniformly varying pitch. Alternative embodiments alsohaving a varying root diameter could also be used.

The FIG. 12 screw has a constant root diameter, a varying thread pitch,and a varying outer diameter of the thread. The FIG. 12 screw comprisestwo discrete portions of different thread pitch and outer threaddiameter; however, alternative embodiments could have a uniformlyvarying pitch/outer diameter. Alternative embodiments also having avarying root diameter could also be used. The pitch of the FIG. 12threads is typically in the range 1 mm to 2 mm at the leading (tip) end,and 2 mm to 4 mm at the trailing (head) end. The FIG. 12 screw willtypically cause a relative distraction of bone portions 12, 14 of 1 mmto 2 mm per rotation.

As explained above, the steeper the angle of the thread, the greater theresistance of the screw to removal in the direction of that edge.Steeply sloping thread edges with respect to the root (like those of theFIGS. 9 and 10 embodiments) will provide an abrupt resistance to axialmovement, as compared to more smoothly sloping edges, which would easethe axial movement of the screw using the principal of the inclinedplane. Therefore, the threads at the leading end will provide a highresistance to movement in the direction of insertion, due to theperpendicular leading edges. The threads at the trailing end willprovide a high resistance to axial movement in the direction opposite tothe direction of insertion, due to their perpendicular trailing edges.Thus, the screws of FIGS. 11 and 12 resist removal in both axialdirections, due to the leading end threads resisting axial movement inthe direction of insertion, and the trailing end threads resisting axialmovement in the opposite direction.

The screws of FIGS. 7 and 12 all provide a high resistance to axialforce once in the bone, due to having at least some steep edges relativeto the axis of the screw in both axial directions. This is particularlyuseful for use in fragile bones, for example in the elderly, where thebone is so soft that a conventional screw could more easily be pulledthrough the bone.

All the screws of FIGS. 7 to 12 are suitable for distracting a fracture,as they all have screw threads of a smaller pitch at the leading end ascompared to the trailing end.

It should be noted that it is not only the FIG. 5 or FIG. 6 design(varying root diameter) that has the advantage that the trailing threadscut into previously uncut bone. The embodiments having a constant rootdiameter but increased outer diameter of the threads at the trailing end(such as those shown in FIGS. 8, 10 and 12) also have this advantage.The larger diameter threads at the trailing end cut into previouslyuncut bone to secure the screw more firmly in the bone.

The bone fixing devices of all embodiments may be metallic ornon-metallic, and the invention is not limited to the use of anyparticular material. The bone fixing device may be made of abioabsorbable material. Examples of suitable bioabsorbable materialsinclude polylactic acids and polyglycolic acids; however any othermedically recognised bioabsorbable material could be used.

The fixing device may or may not be provided with a coating. A possibleexample of a suitable coating is hydroxyapatite. This can be applied tothe fixing device by dipping the fixing device in the coating andallowing the coating to dry. Hydroxyapatite is a common calcium saltthat is also found naturally in bone. The presence of a hydroxyapatitecoating on the fixing device encourages the surrounding bone to grow,both on to the fixing device itself and, generally, in the vicinity ofthe screw.

In some useful versions of the fixing device, the threads need not varybetween the ends of the device, and FIGS. 20-22 show embodiments thatmaintain the loading on the screw by means of the shapes of the threads,rather than by means of the changes in pitch. Despite the lack of changein pitch of the thread which can be used for active loading of thethreads in a distracted fracture, the embodiments of FIGS. 20-22 will besubjected to loading by the natural bias of the bones tending tocompress the device, which will thereby exert a loading force on thethreads of the screw tending to resist dislodgement of the screw whenimplanted. Referring now to FIG. 20, there is shown a screw havingmodified thread profiles similar to that shown in FIG. 7, although theFIG. 20 screw has a constant root diameter, a constant pitch thread anda constant outer thread diameter.

In the FIG. 20 screw, both the leading and trailing sides of the threadslope between the radially outer tip of the thread and the root; theslope is very steep, and is typically non-linear, in that the slope ismore gradual near the root of the screw, and steeper nearer to theradial edge of the thread. The steeper the slope (i.e. the closer toperpendicular with the root axis) the more difficult it is to remove thescrew from the bone by an axial force. This is because thenear-perpendicular surfaces provide an abrupt resistance to the passageof the screw through the bone, as compared to more gradually slopingsurfaces, where the screw would use the gradual slope to ease its waythrough the bone. Therefore the FIG. 20 screw would be very difficult toremove from the bone, in either axial direction.

FIG. 21 is another version of a screw with rectangular threads similarto the FIG. 9 embodiment, but having a constant root diameter, aconstant pitch thread and a constant outer thread diameter. This screwis suitable for maintaining a fracture.

FIG. 22 shows a further version of screw with a thread profile similarto that of the FIG. 11 embodiment, but having a constant root diameter,a constant pitch thread and a constant outer thread diameter. This screwis suitable for maintaining a fracture.

Modifications and improvements may be incorporated without departingfrom the scope of the invention. For example, any of the screws shown inFIGS. 7 to 12 could optionally have a non-threaded mid-portion (notshown), and/or a varying root diameter (not shown).

Screw 200 and the screws of FIGS. 8, 10 and 12 all have an abrupt changeof diameter; however, the diameter change could alternatively beuniform, such as in screw 100. Any of the designs of screw threads shownin FIGS. 7 to 12 could be combined with any of screws 100 and 200.

All of the screws in FIGS. 7 to 12 can have self-drilling, self-tappingtips; they may be cannulated; they may have non-threaded mid-portions;and they may have a head which does not project outwardly of the surfaceof the root.

Although the examples here are described with reference to wristfractures, the invention could be used for any fracture.

FIG. 13 shows a jig 10 which is being used to define two lines ofinsertion of two threaded bone fixing devices (not shown) into a bone B.In this example, bone B is a radius, and the fixing devices are to beinserted in the head of the radius. However, the invention is notlimited to the use in any particular part of any particular bone.

The head of bone B is typically fractured (fracture lines not shown),and the fixing devices (e.g. bone screws) are to be inserted to hold thefracture fragments together.

The jig 10 has an elongate arm 11 which has the form of an arc. The arm11 has a slot 13 which extends along the length of the arm 11. The slot13 extends all the way through the arm 11.

A first sleeve 20 is coupled to one of the elongate ends of the arm 11such that the arm 11 extends from a lateral side of the sleeve 20. Thefirst sleeve 20 may be coupled to the arm 11 by any suitable means.Preferably, the sleeve 20 is slidably mounted on the arm, for examplethe arm 11 may have a guide slot and the sleeve 20 may be slidablymounted in the slot. The sleeve 20 has an inner bore which is adapted toreceive a first guide wire G1. The first sleeve 20 may be a standardguide/drill sleeve, but any guide means (typically with an aperture toreceive the guide wire or bone fixing device) can be used.

A spacer 15 in the form of an alignment block 15 is coupled to the arm11 by a bolt 116. The spacer 15 is cuboid, and has a bore 17 in whichthe bolt 116 is received. The bolt 116 also passes through the slot 13.A nut (not shown) engages one end of the bolt 116 to hold the spacer 15fixed relative to the arm 11.

When the nut is loosened, the bolt 116 can move within the slot 13 sothat the spacer 15 moves relative to the slot 13; the spacer 15 can alsobe rotated around the axis of the bolt 116 in the plane defined by thearcuate arm 11. This rotation is shown in FIG. 13 by the arrows R.

The spacer 15 also has a further bore 18, which extends through thespacer 15 in a direction perpendicular to the bore 17. The bore 18 goesdirectly between opposite sides of the cuboid spacer 15 in a straightline which is perpendicular to the opposite sides (not at an inclinedangle through the block). Therefore, the bore 18 lies in a planeparallel to the plane of the elongate arm 11. The bore 18 is adapted toreceive a second sleeve 22. Preferably, the second sleeve 22 is slidablymountable and optionally rotatably mountable in the bore 18. The secondsleeve 22 is similar to the first sleeve 20, and has an inner boreadapted to receive a second guide wire G2.

Although just single sleeves 20, 22 are shown in FIG. 13, each of thesecan represent a set of concentric sleeves. For example, sleeve 22 canrepresent an inner sleeve for a guide wire, an intermediate sleeve for adrill and an outer sleeve for a fixing device. The same applies tosleeve 20.

The second sleeve 22 defines a second line of insertion I2 and the firstsleeve 20 defines a first line of insertion I1. The lines of insertionI1, I2 are continuations of the axes of the sleeves 20, 22 into thebone.

The lines of insertion I1, I2 lie in parallel planes, because theirrelative positions are defined by the sleeves 20, 22, which are in turndefined by the jig 10. The first line of insertion I1 always lies in theplane of the elongate arm 11, as the first sleeve 20 is fixed (apartfrom any slidable mounting) to the end of the arm 11, the arm 11extending from a lateral side of the first sleeve 20.

As explained above, the bore 18 lies in a plane parallel to the plane ofthe elongate arm 11; therefore the second line of insertion I2 alwayslies in a plane parallel to the plane of the elongate arm 11. This isalways true independent of the selected rotational and translationalposition of the spacer 15. In the FIG. 13 view, the plane of the secondline of insertion I2 is in front of the plane of the elongate arm 11.

The second line of insertion I2 is adjustable relative to the first lineof insertion I1 by altering the rotational and translational position ofthe spacer 15. The angles of the guide sleeves 20, 22 can therefore beadjusted so that the lines of insertion I1, I2 cross when viewed in adirection perpendicular to the parallel planes of the lines of insertionI1, I2 (as seen in the FIG. 13 view).

Because the arm 11 is arcuate (see FIG. 13) no additional rotationaladjustment of the spacer 15 relative to the slot 13 is necessary inorder to ensure that the lines of insertion cross. For example, in someembodiments, rotation of the spacer is guided by the arcuate slot 13 sothat on moving (translating) the spacer 15 along the slot 13, the spacer15 is automatically rotated so that the axis of the bore 18 is alwaysperpendicular to the part of the slot 13 in the vicinity of the spacer15. This could be achieved by providing the spacer 15 with one or morelateral projections adapted to engage the slot 13. These embodiments canprovide jigs which are simple to operate, since a change intranslational position of the spacer along the arcuate jig automaticallyadjusts the spacer's rotational position so that the respective lines ofinsertion cross in the desired location when seen from the FIG. 13direction. However, the capability to rotate the spacer 15 isadvantageous, as this allows a very precise selection of the angle ofinsertion (several alternative options for the second line of insertionare shown in dotted lines in FIG. 13).

The position of the bore 18 in the spacer 15 is preferably selected suchthat the distance between the plane of the elongate arm 11 (the plane ofthe first line of insertion) and the parallel plane in which the bore 18lies (the plane of the second line of insertion) is greater than orequal to the diameter of the bone fixing device (the outer threaddiameter, if threaded). The reason for this will be explained withreference to FIGS. 15 and 16. In FIG. 15, D represents the diameter ofthe fixing devices, and in FIG. 16, RD represents the root diameter ofthe fixing devices, and OD represents the outer (thread) diameter of thefixing devices.

FIG. 15 shows a view from above of two non-threaded bone fixing devicesS1, S2 which have been inserted along respective lines of insertion I1,I2. The tips of the fixing devices and the lines of insertion I1, I2 areangled into the page. The lines I1, I2 also represent the positions ofthe parallel planes of the lines of insertion in this view. In FIG. 15,the distance between the parallel planes is equal to the diameter D;therefore the fixing devices will just touch, but they will not collide.

FIG. 16 shows a further embodiment where the bone fixing devices S3, S4are threaded. In this embodiment, the distance between the parallelplanes is equal to the outer (thread) diameter OD, and the outer threadsof the inserted fixing devices will just touch but not interlock.

Both FIGS. 15 and 16 show how two bone fixing devices can be insertedinto positions where they just touch but do not collide.

This is advantageous, as one fixing device is able to lean against theother; one fixing device effectively buttressing the other. Thisprovides additional support for the bone fixing devices, which helps tokeep them in the bone. In the threaded embodiments this support isadditional to the friction between the threads and the bone. The fixingdevices do not have to be literally touching each other to achieve thiseffect; bone fixing devices a small distance apart could also achievethis effect. The invention encompasses both literally touchingembodiments and other embodiments in which the bone fixing devices passclose together.

FIG. 15 illustrates that the bone fixing devices are not necessarilythreaded, and can be simple rods.

In use, the position of the first line of insertion is selected and afirst guide wire G1 is inserted (e.g. using a guide sleeve) to definethe first line of insertion I1. Next, a hole is drilled for the firstfixing device using a cannulated drill (and also typically a drillsleeve). Next, a first fixing device is inserted into the bone over theguide wire G1 into the hole drilled by the drill (optionally using a tapif the fixing device is not self-tapping). In this method, typically anappropriate sized guide/drill sleeve is selected for each step.

Next, the guide sleeves 20, 22 are coupled to the jig 10 and thisassembly is then positioned as shown in FIG. 13, with the first sleeve20 being inserted over the protruding part of the guide wire G1. Ascrewdriver may be held in the first sleeve 20 so that it engages thefirst fixing device during the subsequent steps, to provide additionalstability to the assembly whilst the second line of insertion isdefined.

Next the nut (not shown) is loosened and the spacer is moved relative tothe slot 13 to a desired translational and rotational position so thatthe second guide sleeve 22 defines a second line of insertion I2.

The surgeon typically ensures that the second line of insertion I2crosses the first line of insertion I1 when viewed in a directionperpendicular to the parallel planes of the lines of insertion I1, I2(i.e. in the direction of the front view of FIG. 13).

Once the second line of insertion I2 has been determined, the nut istightened against the bolt to fix the rotational and translationalposition of the second sleeve 22. A second guide wire G2 is insertedthrough the second sleeve 22 and into the bone along the second line ofinsertion I2.

As explained above, the second sleeve 22 can represent a set ofconcentric sleeves, and the second guide wire G2 is typically insertedthrough an inner sleeve. Next, the inner sleeve can be removed, and ahole is drilled in the bone using a cannulated drill inserted over thesecond guide wire G2 using an intermediate-sized sleeve to guide thedrill. Next, that sleeve is removed and an outer sleeve is used to guidethe insertion of the second fixing device into the bone. If the fixingdevice is not self-tapping, a tap can be used to create space for athread in the bone before insertion of the second fixing device; the tapcan also be guided by the outer sleeve.

The bone fixing devices are typically cannulated bone screws S3, S4 andthe guide wires G1, G2 guide the paths of the bone fixing devices in thebone. Because the lines of insertion have been accurately defined by thejig 10, the fixing devices S3, S4 can be positioned such that they passclosely together, without colliding (optionally even touching eachother). This provides additional support to prevent the fixing devicesS3, S4 coming loose and falling out of the bone. One fixing deviceeffectively buttresses the other, which strengthens the connection ofboth fixing devices to the bone.

In a slightly modified method, the jig 10 and guide sleeves 20, 22 canbe used to insert the first guide wire G1 and the first fixing deviceinto the bone, instead of the jig 10 first being used after these havebeen inserted.

In some versions of the method, the jig 10 and sleeve 20 may be used toinsert the first fixing device but not the first guide wire G1.

In all methods, it is advantageous to use some sort of guide sleeve(whether or not attached to the jig 10) to aid insertion of the guidewires, drill and fixing devices, to protect the surrounding tissues.

FIG. 14 shows an alternative embodiment of the invention, where thespacer 114 is modified to include more than one guide bore. In thisembodiment, two parallel guide bores, 318, 418 are provided. The guidebores 318, 418 are adapted to receive respective sleeves 122, 124, whichdefine lines of insertion of respective guide wires G3, G4. Because theguide bores 318, 418 are parallel, the lines of insertion they definedwill not intersect and screws inserted through sleeves 122, 124 will notcollide with each other. The guide bores 318, 418 may both lie in asingle plane parallel to the plane of the arm 11 (i.e. side by side inthe FIG. 13 view), or the guide bores 122, 124 may each lie in differentplanes parallel to the plane of the arm 11 (i.e. on in front of theother in the FIG. 13 view). The FIG. 14 embodiment may be particularlyuseful when the bone has fractured into many fragments, as including anextra fixing device can help to ensure that more of the fracturefragments are held together.

FIGS. 17 to 19 show alternative embodiments of the invention. FIG. 17shows a modified arm 111 which includes a stepped portion 115. Thestepped portion 115 divides the arm 111 into two portions which lie inparallel planes P5, P6; the stepped portion is an intermediate part ofthe arm 111 which is perpendicular to both portions of the arm 111. Whenseen from the front (like the FIG. 13 view), the P6 plane would be infront of the P5 plane. Therefore in this embodiment, the stepped arm 111functions as a spacer, creating two parallel planes without the need fora separate spacer component 114.

First and second sleeves 520, 522 are attached to the arm 111. Only thetop part of the sleeves 520, 522 are shown for clarity, but the sleevesactually extend downwards into the paper and towards each other, alongthe lines of insertion I5, I6. The first sleeve 520 is attached to thearm 111 so that the arm 111 extends from a lateral side of the sleeve520 (similarly to the FIG. 13 embodiment). Therefore, the first sleevedefines a line of insertion I5 which lies in a plane P5 which iscoplanar with the plane its end of the arm 111.

The second sleeve 522 is attached to a lateral side of the arm 111. Thesecond sleeve 522 may be clamped onto the arm 111 by a clamp (not shown)that extends around the end of the arm 111. The second sleeve 522 may berotatably and/or slidably mounted on the arm 111, or alternatively itmay be fixed relative to the arm 111. Since the second sleeve 522 isattached to a lateral side of the arm 111, the line of insertion I6defined by the sleeve 522 will lie in a plane P6 which is in front ofthe plane P6 of that end of the arm 111 (when viewed from the front).However, the line of insertion I6 is parallel to the plane P6.Therefore, the lines of insertion I5, I6 lie in respectively parallelplanes.

FIG. 18 shows a further embodiment having an arm 211 with a steppedportion 215 defining two arm portions in parallel planes P7, P8, andfirst and second sleeves 320, 322 attached (e.g. slidably mounted) tothe arm. This embodiment is the same as the FIG. 17 embodiment in mostrespects, except that the second sleeve 322 is attached to the arm 211so that the arm 211 extends from a lateral side of the second sleeve322. Therefore, in this embodiment, the lines of insertion I7, I8defined by the sleeves 320, 322 will both lie along the parallel planesP7, P8 defined by the arm 211. The first and second sleeves 320, 322 arenot rotatably mounted on the arm 111. However, in alternativeembodiments, one or both of the first and second sleeves 320, 322 arerotatably mounted.

FIG. 19 shows a further embodiment of a jig having a non-stepped arm311. The arm 311 is provided with two spacers 214, 314, which may besubstantially the same as either of the spacers 15, 114 described above.The spacers 214, 314 are provided with respective sleeves 420, 422. Inthis view, the spacers 214, 314 are located at or near opposite ends ofthe arm, but one or both spacers is preferably translatable along thelength of the arm 311 (e.g. by providing a slot as shown in the FIG. 13embodiment).

The spacers 214, 314 are provided on opposite planar faces of the arm311, and define two lines of insertion I9, I10, both of which lie inmutually parallel planes P9, P10; these planes are also parallel to thearm 311. At least one of the spacers 214, 314 is rotatable relative tothe arm 311, so that the lines of insertion I9, I10 can be made to crosswhen viewed in a direction perpendicular to the parallel planes P9, P10.Thus, in this embodiment, the two spacers 214, 314 together define thespacing of the parallel planes.

In some embodiments, a stepped arm and a separate spacer component canboth be used in conjunction to provide the two parallel planes of thelines of insertion.

The arms 111, 211, 311 could be either straight or arcuate when viewedfrom a front view perpendicular to the top view shown in these figures.

Modifications and improvements may be incorporated without departingfrom the scope of the invention. For example, the jig 10 need not be inthe shape of an arc. In an alternative embodiment, the jig 10 could bestraight.

In some embodiments, the first guide sleeve could be rotatably mountedon the arm and the second guide sleeve could be rotationally fixed withrespect to the arm.

In some embodiments, the sleeves 20, 22 can comprise components of thejig 10, e.g. one or both of the sleeves may be permanently attached tothe jig 10. In other embodiments, the sleeves 20, 22 are attachable toand removable from the jig 10 (e.g. by being slidably mounted on thearm/spacer). Although not shown in FIG. 13, an eye-member could beprovided on the end of the arm 11, so that the first sleeve 20 can beslidably mounted in the eye member.

In further alternative embodiments, the arm could be extendible. Anextendible arm could provide an alternative to a slotted arm, as thiswould also enable relative translation of the two guide sleeves. In someembodiments, the arm may be both slotted and extendible.

In further alternative embodiments, the jig is adapted to allowinsertion of bone fixing devices at locations spaced apart bysignificant distances. Such embodiments provide an increased choice ofrelative angles and positions of the two fixing devices. In theseembodiments, the fixing devices do not necessarily touch or even comeclose to each other, and the surgeon can still be confident that nocollision will occur.

As illustrated in FIG. 15, the bone fixing devices are not necessarilythreaded, and can be rods.

1. A bone fixing device for distracting a fracture, the bone fixingdevice having a body with a leading end and a trailing end, the bonefixing device being threaded at least at the leading end and at thetrailing end; wherein the pitch of the threads at the trailing end isgreater than the pitch of the threads at the leading end. 2-3.(canceled)
 4. A bone fixing device as claimed in claim 1, wherein thetrailing end has a head which is flush with the rest of the body.
 5. Abone fixing device as claimed in claim 1, wherein the body has a greaterdiameter at the trailing end than at the leading end. 6-9. (canceled)10. A cannulated bone fixing device as claimed in claim
 1. 11-12.(canceled)
 13. A bone fixing device as claimed in claim 1, wherein thebone fixing device has a longitudinal axis and at least one side of atleast one of the threads has a portion that is steeply inclined relativeto the longitudinal axis.
 14. (canceled)
 15. A bone fixing device asclaimed in claim 13, wherein each thread has a side having a steeplyinclined portion facing the nearest end of the screw to that thread.16-18. (canceled)
 19. A bone fixing device as claimed in claim 13,including at least one thread having a side having a steeply inclinedportion facing one axial direction and at least one thread having a sidehaving a steeply inclined portion facing the opposite axial direction.20. A bone fixing device as claimed in claim 13, wherein the steeplyinclined portion is substantially perpendicular to the longitudinalaxis. 21-23. (canceled)
 24. A bone fixing device as claimed in claim 1,comprising a bioabsorbable material. 25-26. (canceled)
 27. A method oftreating a fracture resulting in at least two bone portions, the methodcomprising distracting the fracture to hold the bone portions apartunder tension.
 28. A method of treating a fracture as claimed in claim27, comprising engaging a bone fixing device as claimed in claim 1 intoa fractured bone to distract the fracture.
 29. (canceled)
 30. A methodas claimed in claim 28, including the steps of inserting a guide wireinto the bone and subsequently inserting the bone fixing device over theguide wire. 31-32. (canceled)
 33. A jig for positioning first and secondbone fixing devices, the jig defining first and second lines ofinsertion for the first and second bone fixing devices respectively,wherein the lines of insertion lie in parallel planes and wherein thelines of insertion cross when viewed in a direction perpendicular to theparallel planes.
 34. A jig as claimed in claim 33, wherein the jigdefines more than two lines of insertion. 35-36. (canceled)
 37. A jig asclaimed in claim 33, wherein the parallel planes have a minimumseparation equal to the diameter of the bone fixing devices.
 38. Anassembly comprising a jig as claimed in claim 33 and first and secondbone fixing devices, wherein the bone fixing devices are at leastpartially threaded.
 39. An assembly as claimed in claim 38, wherein theparallel planes have a minimum separation equal to the outer threaddiameter of the bone fixing devices.
 40. A jig as claimed in claim 33,wherein the orientation of the second line of insertion is variablerelative to the orientation of the first line of insertion. 41.(canceled)
 42. A jig as claimed in claim 33, wherein the jig includes anarm that extends in a lateral direction with respect to at least one ofthe lines of insertion. 43-44. (canceled)
 45. A jig as claimed in claim42, wherein the first and second lines of insertion are defined byrespective first and second guide means coupled to the arm. 46-47.(canceled)
 48. A jig as claimed in claim 42, wherein the jig includes aspacer adapted to space the parallel planes of the lines of insertionapart from each other.
 49. A jig as claimed in claim 48, wherein thespacer is an individual component distinct from the arm.
 50. A jig asclaimed in claim 48, wherein the spacer comprises a block having a guidebore adapted to receive a guide sleeve.
 51. (canceled)
 52. A jig asclaimed in claim 48, wherein the spacer is rotatably and translatablymounted on the arm.
 53. A jig as claimed in claim 42, wherein the arm isarcuate.
 54. A jig as claimed in claim 48, wherein an elongate apertureis provided in the arm and the spacer is translatable along the elongateaperture.
 55. A jig as claimed in claim 54, wherein the elongateaperture is arcuate, and wherein the spacer is rotationally coupled tothe elongate aperture, such that as the spacer translates along theaperture, the spacer rotates with the curvature of the aperture.
 56. Ajig as claimed in claim 55, wherein the spacer comprises a block havinga guide bore adapted to receive a guide sleeve and wherein ontranslation of the spacer, the spacer rotates such that the guide boreis always perpendicular to a tangent to the elongate aperture at thelocation of the spacer.
 57. (canceled)
 58. A jig as claimed in claim 42,wherein the arm comprises a first portion having a first planar surfaceand a second portion having a second planar surface aligned parallel tothe first planar surface, and wherein the second portion is steppedrelative to the first portion.
 59. A jig as claimed in claim 48, whereinthe spacer comprises a part of the arm.
 60. (canceled)
 61. A jig asclaimed in claim 42, being provided with at least one guide means thatis rotatably and translatably mounted on the arm.
 62. A jig as claimedin claim 42, wherein the arm is extendible.
 63. A method of positioningfirst and second bone fixing devices relative to each other, the methodincluding the steps of defining first and second lines of insertion forthe first and second bone fixing devices respectively, wherein a jig isused to define the position of the second line of insertion relative tothe first line of insertion such that the lines of insertion lie inparallel planes and such that the lines of insertion cross when viewedin a direction perpendicular to the parallel planes.
 64. (canceled) 65.The method as claimed in claim 63, wherein the separation of theparallel planes is at least as large as the diameter of the bone fixingdevices.
 66. (canceled
 67. The method as claimed in claim 63, whereinthe bone fixing devices are inserted at locations in which they are incontact with each other.
 68. The method as claimed in claim 63, whereinthe fixing devices are at least partially threaded and the separation ofthe parallel planes is at least as large as the outer thread diameter ofthe bone fixing devices.
 69. The method as claimed in claim 68, whereinthe separation of the parallel planes is equal to the outer threaddiameter, so that when the first and second fixing devices are insertedalong their respective lines of insertion, the threads on the first bonefixing device are in contact with the threads on the second bone fixingdevice.
 70. The method as claimed in claim 63, including the steps ofinserting first and second guide wires into the bone along therespective first and second lines of insertion and inserting the firstand second bone fixing devices over the first and second guide wiresinto the bone.
 71. The method as claimed in claim 63, wherein the jigincludes first and second guide means which define the respective firstand second lines of insertion and the method includes the step ofvarying the relative orientation and/or spacing of one of the guidemeans relative to the other.
 72. (canceled)
 73. A method of positioningfirst and second bone fixing devices in a bone such that they are indirect contact with one other.
 74. A bone fixing device for treating afracture being at least partially threaded, wherein at least one of thethreads has a portion that is steeply inclined relative to thelongitudinal axis of the bone fixing device, wherein the steeplyinclined portion faces the leading end of the bone fixing device.
 75. Abone fixing device as claimed in claim 74, wherein at least one furtherthread has a portion steeply inclined relative to the longitudinal axisof the bone fixing device, wherein the steeply inclined portion facesthe trailing end of the bone fixing device.
 76. A bone fixing device asclaimed in claim 74, wherein the at least one steeply inclined portionis perpendicular to the longitudinal axis of the bone fixing device. 77.A method of treating a fracture, comprising engaging a fixing deviceinto at least two bone portions of the fracture to maintain the relativeposition of the bone portions.